This application relates generally to a system and method for banding off a mobile node and more particularly to handoff mechanisms to support real-time delay-critical services in next generation wireless networks.
In data networks, such as Internet Protocol (IP) networks, users are typically assigned to a particular class of service (such as Platinum, Gold, or Silver) based on a service level agreement (SLA) with their service provider. In a fixed network, it is relatively easy to engineer and assign the user an appropriate amount of network resources so that the SLA can be maintained at all times. However, mobility and the air-interface being utilized make the problem more difficult because the network resources have to be reassigned and/or renegotiated as the user moves from one cell to another. Additionally, the inherent hostile nature of the air-interface makes it difficult to predict and react accordingly to the changes in the radio frequency (RF).
Historically, there have been two methods to support mobility across wireless cells. In the first method, the mobile is in the full control of the decision making and the target selection process while moving from one cell to the other. In Global Systems for Mobile Communications (GSM) or North American Time Division Multiple Access (NA TDMA) terminology, this process is known as reselection. In a reselection process, the mobile node and the network have a master-slave relationship where the mobile node decides which cell serves its interest best. The network does not really have control over the target cell selection and so it is alerted to the mobile node's decision only after the target cell is selected. As a result, reselection is typically more time consuming from a network resource allocation point of view. Also, reselection during an active session requires the network to temporarily buffer the data destined for the mobile node. Additionally, the target cell may not even have enough resources to address the resource needs of the mobile node.
In the second method, the network, along with input from the mobile node, decides when and where to handoff the mobile node. Handoff refers to the transfer of an ongoing wireless call from one transmission site (cell) to another without disconnecting the call. This method requires constant monitoring of the mobile node's signal strength as well as complex management of target selection and network resource assignment. Network directed handoff also requires more messaging over the air compared to reselection. However, this kind of mobility support can work faster because the target is known before the actual handoff takes place. Also, the resource allocation and appropriate reservation can be done at the target to meet the mobile node's demand. In a variation of this scheme in GSM and NA TDMA, the mobile node assists the network by periodically sending it RF related information regarding the mobile node's neighboring cells. This facilitates the decision making process at the network and is called Mobile Assisted Handoff (MAHO).
The reselection based mobility works fine when the mobile node is idle or in a non-real time active session. However, as previously mentioned, reselection may result in considerable delays. Thus, buffering data for a synchronous real time application (such as voice or video) during this delay interval is not recommended. Because the reselection mechanism does not have any control over the availability of the network resources at the target cell, during the few seconds of reselection related delay, several voice packets may be dropped resulting in audible speech clipping. Additionally, in current data networks, the reselection process does not prioritize resources based on the user's SLA. To address Quality of Service (QoS) requirements for real-time, delay-sensitive multimedia services, the handoff mechanism needs to be optimized and enhanced in next generation wireless data (IP) networks.
Therefore, an improved system and method is desired to reduce or eliminate the aforementioned complexities and limitations.